The broad objectives of this project are: (a) to study the relationship between enzyme structure and function, (b) to study the regulation of enzyme activity at the molecular level, and (c) to study the regulation of biosynthesis of enzymes. In order to carry out these experiments, studies on the TPN ion-specific isocitrate dehydrogenase from Azotobacter vinelandii will be used as a model for structure-function relationships. For the control of enzyme activity, the in vitro differentiation of mouse embryonal carcinoma cells will be employed. The broad objectives outlined above have significance in leading to a better understanding of the regulation and control of other biological processes.